Each gateway is configured with a maximum number of failed call attempts before traffic to the gateway is limited. The default number of attempts is ten, but this value can be changed by using a Windows Management Instrumentation (WMI) script. Limiting call attempts discourages malicious efforts to tie up incoming lines.
For a particular call, a given gateway cannot be attempted more than once. If all gateways that serve a particular route are marked as unavailable, the server drops the call and notifies the client. You can also configure a gateway to be removed from the selection logic for some period of time. The unresponsive gateway is removed from the list of available gateways for increasing periods of time, up to a maximum of 60 minutes, during which time the server repeatedly attempts to elicit a positive response. After receiving a positive response, the server returns the gateway to the list of available gateways.